Aminophenol compounds represented by the formula (1) and salts thereof:
(wherein each of R1 and R2, which may be the same or different, is a hydrogen atom, a substituted or unsubstituted lower alkyl group, a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group; R1 and R2, taken together with the adjacent nitrogen atom, may form a 5- or 6-membered heterocycle with or without other intervening heteroatoms; the heterocycle may be substituted by 1 to 3 substituents selected from the group consisting of a hydroxyl group, a substituted or unsubstituted lower alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted heterocyclic group and a substituted or unsubstituted heterocyclic group-substituted oxy group; and the hydroxyl group in the formula (1) is substituted on the second or the fourth position of the phenyl ring) are useful as a synthesized intermediate for various pharmaceutical agents (preferably antitubercular agents) and agrichemicals.
Heretofore, as a method of producing aminophenol compounds, for example, methods shown in the following Reaction scheme-1 and Reaction scheme-2 are known (Stephen L. Buchwald et al., Organic Letters, vol. 4, 2885 (2002)).

In the above-mentioned schemes, the group —NR′R″ is a dibutyl amino group, a N-methylanilino group, a morpholino group, a 4-methylpiperidinyl group, a 4-hydroxypiperidinyl group, a 4-methylanilino group, a 4-methoxyanilino group and a 3,4-dimethoxyanilino group, and R is a protecting group of a hydroxyl group.
These methods, however, have various defects and therefore not suitable for an industrial production method.
For example, the method shown in the Reaction scheme-1 requires expensive basic or metal catalysts such as a palladium catalyst, aromatic triflate and a copper catalyst. The method shown in the Reaction scheme-2 requires a complicated step of protecting the hydroxyl group of phenol and then removing the protecting group.
Kazuo Haga et al. (Bull. Chem. Soc. Jpn., 57, 1586 (1984) and Bull. Chem. Soc. Jpn., 59, 803-807 (1986)) disclose that the reaction of 1,4-cyclohexanedione and a secondary amine in the presence of an acid catalyst does not afford an aminophenol compound or if do, the yield is only 4 to 12%, and the main product of the reaction is an aniline compound.
A. Reiker et al. (Tetrahedron, 23, 3723 (1967)), J. Figueras et al. (J. Org. Chem., 36, 3497 (1971)) and JP-A-62-29557 disclose that the reaction of 1,4-benzoquinone and a primary amine in the presence of an acid catalyst affords a quinone monoimine compound, and the generated quinone monoimine compound must be further reduced in order to produce the objective aminophenol compound.